Development of sodium alginate/fructooligosaccharides (FOS) microcapsules functionalized with Lactobacillus rhamnosus and phenolic extracts from uvaia

Probiotics play an essential role in host health. However, their viability can be compromised by adverse conditions during processing. This study aimed to develop sodium alginate and fructooligosaccharide (FOS) microcapsules functionalized with Lactobacillus rhamnosus and phenolic extract from uvaia (Eugenia pyriformis Cambess), using spray drying. The process was carried out at 70 °C (outlet temperature), with a feed rate of 0.4 L/h and air flow rate of 1.4 m³/L. Eight formulations were tested, varying the encapsulating matrix (FOS, alginate, or both), the type of phenolic extract (pulp – PU or seed – SU), and the presence of CaCl₂ (7.7 mmol) as a gelling agent. Formulations G1 and G2 contained only FOS (20 g/L) and phenolic extract from pulp or seed, respectively; G3 and G4 combined sodium alginate (20 g/L) and FOS (20 g/L) (88:12 v/v) with CaCl₂ and phenolic extract from pulp and seed, respectively; G5 and G6 used sodium alginate (20 g/L) and FOS (20 g/L) in a single solution with CaCl₂ and phenolic extract from pulp and seed, respectively; G7 and G8 contained only alginate and phenolic extract from pulp and seed, respectively. The probiotic strain was added to all formulations at a final concentration of 5.51 × 10⁷ CFU/mL. Bacterial viability (log CFU/g), total phenolic content (TPC, mg gallic acid equivalent – GAE/g), antioxidant capacity (ABTS, mmol Trolox equivalent – TE/g), and thermogravimetric (TGA) and structural (FTIR) analyses were performed. L. rhamnosus counts ranged from 4.81 to 7.63 log CFU/g, with G5 showing the highest viability, suggesting a synergistic effect between polysaccharides and ionic gelation in preserving viability. In contrast, G2 and G6, both containing SU extract, showed lower viability, possibly due to the antimicrobial effect of uvaia seed phenolics. TPC values ranged from 1.91 to 7.59 mg GAE/g, with higher concentrations in G2, G4, and G6, all with SU extract, which also exhibited higher antioxidant capacity, especially G4 (79.95 mmol TE/g). TGA analysis revealed greater thermal stability in microcapsules with higher alginate content, particularly G8, with a residual mass of 40.52% at 600 °C. The presence of CaCl₂ also contributed to the thermal stability of FOS-containing samples. FTIR spectra indicated structural interactions between FOS, alginate, and phenolic compounds. Overall, the results indicate that strategic selection of encapsulating agents and bioactive components can optimize the functional and protective properties of probiotic microcapsules, with potential applications in functional food and nutraceutical formulations.